Tsipras makes last-ditch appeal to Greeks for a No vote
Prime Minister Alexis Tsipras has urged Greeks in another televised address to reject the tough terms of an aid deal offered by international creditors to keep the country afloat.
His European partners say a 'No' vote will jeopardise Greece's membership of the euro.
Mr Tsipras says they are bluffing, fearing the fallout for Europe and the global economy. But a 'Yes' vote may bring him down, ushering in a new period of political instability for a country reeling from five days of shuttered banks and rationed cash withdrawals.
Three new opinion polls have put the 'Yes' vote marginally ahead - a fourth put the 'No' camp 0.5pc in front - but all were within the margin of error.
Mr Tsipras seized on a report by the IMF - which argued that Greece's massive public debt could not be sustained without significant writedowns - as vindication of his rejection of the lenders' terms.
Finance Minister Yanis Varoufakis called the IMF report "music to our ears". Regardless of the outcome of the referendum, Greece will need €50bn as well as a massive debt writedown, the report said.
Europe has fired fresh warnings of the costs of a 'No' vote in a referendum called at just eight days' notice after the breakdown of talks with the European Commission, the IMF and the European Central Bank.
Commission President Jean-Claude Juncker dismissed Mr Tsipras's claim that his government would be able to negotiate more favourable terms if Greeks backed his rejection.
"If the Greeks will vote 'No', the Greek position is dramatically weakened," Mr Juncker insisted.
Tomorrow's ballot could decide whether Greece gets another last-ditch financial rescue in exchange for more harsh austerity measures or plunges deeper into economic crisis.
Mr Tsipras' opponents have pointed to the fact that the referendum is on a deal that is no longer on the table, accusing him of recklessly endangering the country's future.
Greece's top administrative court, however, rejected an appeal against the referendum by two Greek citizens, who argued that the constitution bars plebiscites on fiscal issues and that the question is too complex.
The 'No' campaign has directed much of its venom at Germany, Greece's biggest creditor.
One poster plastered in central Greece shows a picture of German Finance Minister Wolfgang Schaeuble with the slogan: "For five years he's been sucking your blood. Tell him NO now."